The present invention relates to a ceramic heater which is widely used in, for example, a field related to biotechnology such as molecular biology and genetic engineering and a field of physical and chemical research with regard to medical treatment, the food industry, or the like.
In a field such as a field related to biotechnology such as molecular biology and genetic engineering, a field of physical and chemical research with regard to medical treatment, the food industry, or the like, is a constant-temperature vessel is indispensable for heating a sample in a test tube or a microtube and keeping the sample at a fixed temperature. Such a constant-temperature vessel needs high temperature precision. This is because most experiments in the above fields concern enzyme reactions, each enzyme has an optimum temperature, and an enzyme is inactivated at a temperature higher than a definite temperature. Further, in a field of genetic engineering, when mutually complementary nucleic acid molecules, or the like, are subjected to annealing, or when nucleic acid molecules each having two chains are dissociated so as to have single chain, it is necessary to control temperatures strictly.
Further, such a constant-temperature vessel is required to reach a predetermined temperature in a short period of time. If the time is too long, it is not efficient because an unacceptable time is required for a completion of one experiment when a temperature of the constant-temperature vessel has to be frequently changed as in a PCR (Polymerase Chain Reaction) method, which is a genetic amplification method used widely in genetic engineering. Further, when a plurality of experiments are conducted in parallel and each constant-temperature vessel has an independent predetermined temperature, the experiments cannot be effectively conducted if the time until a temperature reaches a predetermined one is too long.
As a constant-temperature vessel having such properties, there have conventionally been used a constant-temperature water vessel, an aluminum block constant-temperature vessel, or the like. A constant-temperature water vessel is a cistern being provided, therein, with a heater for heating water. In an aluminum block constant-temperature vessel is an aluminum block having a cavity for receiving an object to be heated by a heater on the outside.
In recent years, there has been proposed a heater in which a heating element is embedded in a ceramic block of aluminum nitride and a cavity for receiving an object to be heated on a surface of the block, which make use of an excellent heat conductivity of aluminum nitride (Japanese Patent Laid-Open 6-210189).
However, there are some problems. Since a test tube, or the like, is directly put in a liquid in the constant-temperature water vessel, the outer wall of the test tube gets wet and water on the outer wall has to be wiped off before the next step. Besides, water on the outer wall sometimes enters in the test tube, and it causes a contamination.
With respect to an aluminum block constant-temperature vessel, it has low temperature precision and a variance in temperature distribution is large because it is heated by a heater on the outside. Accordingly, it is difficult to control conditions for an experiment. Sometimes, a temperature in the constant-temperature vessel exceeds a predetermined temperature, and an enzyme is prone to be inactivated in an enzyme reaction.
Further, both a constant-temperature water vessel and an aluminum block constant temperature vessel need a long time to reach a predetermined temperature. For example, it takes about 100 seconds to raise 100.degree. C. Accordingly, a time length until the constant-temperature vessel reaches a predetermined temperature is a rate-determining condition of an experiment, and the experiment cannot effectively proceed.
On the other hand, a ceramic heater using aluminum nitride solves the problems that an outer wall of a test tube gets wet and that a variance in temperature distribution is large, a temperature of the ceramic heater reaches a predetermined one in a shorter time. However, there is a problem that it takes about 50 seconds for a rise of 100.degree. C.
In view of these situations, the present invention aims to provide a ceramic heater which can be heated up to a predetermined temperature in a short time and is excellent in temperature precision without hindrance to an enzyme reaction, or the like, by keeping the temperature so as not to exceed a predetermined one.